Final answer:
During the post-classical era, the Roman Empire faced cultural changes with the rise of Christianity, transformation of its senatorial class, expansion of bureaucracy, and fluctuating borders due to barbarian threats, leading to the fragmentation of the western Empire and the continuity of the eastern Byzantine Empire.
Step-by-step explanation:
The post-classical era of the Roman Empire was a time of significant change and transformation. It was during this era, particularly in the late 400s and early 500s, that the Christian Church rose to prominence, affecting cultural and administrative aspects of the empire. The empire's bureaucracy expanded, and the Roman senatorial class evolved into a more localized form of governance for the city of Rome, rather than the entire state. Despite ongoing warfare on the eastern frontier, urban growth persisted in some areas, while in others, public spaces deteriorated. The empire's borders were fluid, as it faced the emerging threat of organized and populous barbarian groups capable of defeating Roman forces, leading to the fragmentation of the western Empire by the end of the fifth century. Meanwhile, the eastern part of the empire, which later became known as the Byzantine Empire, maintained continuity with the Roman past while epitomizing the major shifts during the transition to the Middle Ages.